The mineral-rich east of the Democratic Republic of Congo has been dogged by conflict for more than 30 years, since the 1994 Rwandan genocide.
Numerous armed groups have competed with the central authorities for power and control of the potential fortune in this vast nation.
The instability has sucked in neighbouring countries to devastating effect – notoriously in the 1990s when two huge conflicts, dubbed Africa’s World Wars, resulted in the deaths of millions of people.
What is happening in Goma?
After a rapid advance in the region, fighters from the M23 rebel group have captured almost all of Goma – a major city of more than a million people in the east of DR Congo.
Sitting on the border with Rwanda and the shores of Lake Kivu, it is a vital trading and transport hub that is within reach of mining towns supplying metals and minerals in high demand such as gold, tin and coltan, which is a key component of mobile phones and other consumer electronics.
UN aid agencies have warned of a major humanitarian crisis with shortages of food and water, hospitals overwhelmed by casualties and bodies lying on the streets.
The M23 has also threatened to continue its offensive to the capital, Kinshasa, although analysts say this may be unlikely, as it is 2,600km (1,600 miles) away, on the other side of this vast country.
Who are the M23?
The M23 are led by ethnic Tutsis, who say they needed to take up arms to protect the rights of the minority group.
They say that several previous deals to end the fighting have not been respected – they take their name from a peace agreement that was signed on 23 March 2009.
Shortly after its creation in 2012, the M23 rapidly gained territory and seized Goma – acts that were met with international opprobrium and accusations of war crimes and human rights violations.
It was forced to withdraw from Goma, and then suffered a series of heavy defeats at the hands of the Congolese army along with a UN force that saw it expelled from the country.
M23 fighters then agreed to be integrated into the army in return for promises that Tutsis would be protected.
But, in 2021, the group took up arms again, saying the promises had been broken.
Is Rwanda involved in the fighting?
M23 leader Sultani Makenga is a Congolese Tutsi who previously fought in the Rwandan army.
Rwanda has in the past consistently denied that it supported the M23, but ever since 2012 UN experts have accused it of providing weapons, logistical support and even ultimately commanding the rebels.
DR Congo’s government, as well as the US and France, have also identified Rwanda as backing the group. Last year, a UN experts report said that up to 4,000 Rwandan troops were fighting alongside the M23.
On Friday, Rwandan government spokesperson Yolande Makolo told the BBC that the country’s troops were deployed along its border to prevent the conflict spilling over to its territory.
Rwanda previously said it was being scapegoated and blamed the recent fighting on the Congolese authorities, saying they had refused to enter into a dialogue with the M23.
A peace process, mediated by Angola and involving Rwanda and DR Congo, did result in a ceasefire deal last year, however that soon fell apart and fighting resumed.
What is the connection with Rwanda?
The origin of the current fighting can partly be traced back to the genocide in Rwanda in 1994.
About 800,000 people – the vast majority from the Tutsi community – were slaughtered by ethnic Hutu extremists.
The genocide ended with the advance of a force of Tutsi-led rebels commanded by Paul Kagame, who is now president.
Fearing reprisals, an estimated one million Hutus then fled across the border to what is now DR Congo. This stoked ethnic tensions as a marginalised Tutsi group in the east – the Banyamulenge – felt increasingly under threat.
Rwanda’s army twice invaded DR Congo, saying it was going after some of those responsible for the genocide, and worked with members of the Banyamulenge and other armed groups.
After 30 years of conflict, one of the Hutu groups, the Democratic Forces for the Liberation of Rwanda (FDLR), which includes some of those responsible for the Rwandan genocide, is still active in eastern DR Congo.
Rwanda describes the FDLR as a “genocidal militia” and says its continued existence in the DR Congo’s east threatens its own territory. The Rwandan spokesperson said they wanted to return to Rwanda to “finish the job”.
It accuses the Congolese authorities of working with the FDLR – accusations which DR Congo denies.
Rwanda is unlikely to stay out of DR Congo unless it is satisfied that the FDLR is no longer a threat to itself, or to the Tutsi communities in eastern DR Congo.
What about Congo’s mineral wealth?
DR Congo and multiple UN reports have accused Rwanda of using the conflict as a way of looting Congolese minerals, such as gold and coltan, which is used to make mobile phones and other electronic items such as cameras and inside cars.
In recent years, the M23 has seized several lucrative mining areas and a report by UN experts last December said that around 120 tonnes of coltan was being sent by the M23 to Rwanda every four weeks.
They also noted a huge rise in Rwanda’s mineral exports in recent years, most of which is believed to come from DR Congo.
Rwanda has consistently denied allegations of exploiting DR Congo’s minerals.
What are the UN peacekeepers doing?
A UN peacekeeping mission has been in place since 1999. The current force – known as Monusco – is made up of more than 10,000 troops.
However, of these, only the Force Intervention Brigade is allowed to carry out offensive operations against armed groups. It was this force that helped defeat the M23 in 2013.
Monusco has been the target of anger from ordinary Congolese who see it as failing to do its job. President Félix Tshisekedi, deeming the mission a failure, had asked it to leave by the end of last year.
But the departure was delayed and in December the mission was extended for another year.
The Southern African Development Community (Sadc), a regional grouping of 16 countries, has also deployed a military force to eastern DR Congo, but it has been unable to halt the rebels.
South Africa said 13 of its soldiers had been killed in clashes with rebels as they were trying to stop the advance on Goma. Three Malawian soldiers have also been killed.
Cyril Ramaphosa, South Africa’s president, warned Rwanda that further attacks on its troops would be considered a “declaration of war”.
Rwanda’s President Paul Kagame hit back, accusing South Africa of being part of a “belligerent force” involved in “offensive combat operations”.
The UN said that Uruguay had lost one of its soldiers who was part of the Monusco force.
